<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>Defjs</title>
        <script src="js/def.js"></script>
        <script>
            window.onload = () => {
                $$('#btn').click(() => {
                    console.log('Hello world ...');
                    $$('#div').html('Hello world ...')
                })
            }
        </script>
    </head>
    <body>
        <div id="div">
            
        </div>
        <button id="btn">button</button>
    </body>
</html>